My psoriasis responds really well to 20% coal tar solution mixed in to
Cooper's milking salve when I am not too lazy to use it (Hi Pat!). It smells
dreadful (like a road!) but it really works.  Use a tiny amount 4 times
daily, but rub well in, reduce this to three times a day, then twice etc as
the skin returns to normal and you can often have several treatment-free
days before it starts to recur.  I also had psoriasis on my nipples when
nursing my twins - but mildly - and I think breastmilk *helped*.  I have no
idea whether the above cream/ointment would be OK for the nursing baby, but
perhaps our pharmacist fundis could comment?  Sunlight is also helpful, but
work up from just a minute or two at first to avoid sunburn.

Pamela Morrison IBCLC, Zimbabwe